An interlock system is usually used to prevent a driver who is under the influence of alcohol after a positive result has been obtained for an alcohol test from starting the engine of a vehicle (passenger car, truck, bus, etc.). An interlock system contains for this essentially two components: An alcohol tester, which is usually located inside the vehicle, as well as a control device, which is coupled with the alcohol tester and is permanently installed, for example, under the dashboard of the vehicle and is designed to connect or block the power supply to the starter of the vehicle. The alcohol tester is preferably a breath alcohol tester that is designed as a hand-held device and is connected to the control device via an electric connection cable. As an alternative, the hand-held device may also be coupled with the control device in a wireless manner (for example, via infrared light, Bluetooth or similar protocols).
Such an interlock system usually operates as follows: After switching on the vehicle's ignition, the interlock system prompts the driver to give a breath sample. The test result for the measured breath alcohol concentration, from which the alcohol level can be determined by means of known algorithms, decides whether the starter of the vehicle is released and the engine can be started.
Tampering is possible, in principle, when using an interlock system because, for example, a requested alcohol test is performed by a second person, who is not the driver who is to be checked. To rule out such a possibility of evasion, prior-art interlock systems usually have an alcohol test repeat function. This means that the interlock system prompts the driver again after a randomly generated time interval to perform an alcohol test.
To determine the breath alcohol concentration or the alcohol level, the testing system of an interlock system normally contains an electrochemical sensor system, as it is also used in breath alcohol testers used by the police. This sensor system responds very specifically to alcohol, so that other expired substances or cigarette smoke do not distort the test result.
All the events relevant for the use, for example, date, time, release of a breath sample or refusal to release a breath sample, measured alcohol concentration, engine starts and engine stops, electric bypassing of the interlock system as well as other attempts at tampering are recorded in a memory of the interlock system during the use of the vehicle. These data can be compiled into a protocol and read, for example, by means of a data cable, by which the hand-held device of the interlock system is connected to an external computer. The reading may take place, for example, in an authorized workshop or on site by an authorized mechanic.
DE 197 42 261 A1 describes a device for blocking the operation of a vehicle by a driver who is under the influence of alcohol. The alcohol tester is designed to be attached to a body part (arm or leg) of the driver and to be able to measure the driver's alcohol level by means of an electrochemical gas sensor via the skin permeation. The analyzing unit of the device proper, via which release or blocking of the vehicle takes place, is mounted permanently in the vehicle and communicates with the tester in a wireless manner.
U.S. Pat. No. 7,256,700 B1 pertains to an interlock system, by means of which a vehicle is prevented from being started by a driver who is under the influence of alcohol. The interlock system is coupled with a cell phone or a similar communications means, with which a failed alcohol test is communicated by a verbal message being sent via the cell phone. Furthermore, data, which are stored in the interlock system, can also be sent via the cell phone.
US 2007/0273537 A1 discloses a combined testing and positioning system, which contains, among other things, an interlock system. The interlock system is used in this case in the known manner to prevent a vehicle from being started by a driver who is under the influence of alcohol. The system is equipped, furthermore, with an EMHA (Electronic Monitoring Home Arrest) system, which can communicate with a remote server, for example, via a cell phone. However, data being stored in the interlock system can be communicated to the server via this cell phone as well.
One drawback of the prior-art interlock systems is that these cannot be deactivated or reactivated from a remote center. Many interlock systems are not used to prevent, for example, an offender sentenced because of an alcohol-related offense, from starting his automobile while under the influence of alcohol. Many interlock systems are rather used on a voluntary basis or are used to increase safety, for example, in areas of the transport of heavy loads, the transport of hazardous materials, in school buses, in tourist buses or even in public or private passenger transportation. Should the vehicle be prevented from being started, for example, because of a technical defect of the interlock system or due to a malfunction of or erroneous detection by the alcohol sensor, the driver is not able to start his or her vehicle even though the driver is not under the influence of alcohol.
As was explained above, the driver of a vehicle is usually prompted by the interlock system to perform an alcohol test not only at the beginning of a drive but also during the drive at irregular and randomly determined time intervals. It may therefore happen in case of a sudden malfunction of the interlock system that, for example, a truck transporting hazardous materials cannot be started any more in the middle of the turnpike. The defective interlock system can be released or deactivated in such a case on site only at the interlock system of the vehicle itself by a specially trained and authorized mechanic driving to the “stopped” vehicle and entering a secret release code into the interlock system via a data cable with the corresponding interface of the interlock system, as a result of which the interlock system is released or deactivated and the engine of the vehicle can again be started without a repeated alcohol test being performed. (However, this is possible only if there is no hardware defect, which makes communication with the interlock entirely impossible.) The interlock system must subsequently be repaired and reactivated in a workshop. Should no mechanic be available, the vehicle must be towed to an authorized repair shop in order to have the interlock system released or deactivated there. Both solutions are very time-consuming and lead to high resulting costs.